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author | Oleg Nesterov <oleg@redhat.com> | 2010-06-11 20:04:46 +0200 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2010-06-18 10:46:57 +0200 |
commit | 8d1f431cbec115a780cd551ab1b4955c125f8d31 (patch) | |
tree | f71e707f0ff495582bd2f43017c87b2ac6ec519d /kernel/posix-cpu-timers.c | |
parent | 0bdd2ed4138ec04e09b4f8165981efc99e439f55 (diff) | |
download | linux-stable-8d1f431cbec115a780cd551ab1b4955c125f8d31.tar.gz linux-stable-8d1f431cbec115a780cd551ab1b4955c125f8d31.tar.bz2 linux-stable-8d1f431cbec115a780cd551ab1b4955c125f8d31.zip |
sched: Fix the racy usage of thread_group_cputimer() in fastpath_timer_check()
fastpath_timer_check()->thread_group_cputimer() is racy and
unneeded.
It is racy because another thread can clear ->running before
thread_group_cputimer() takes cputimer->lock. In this case
thread_group_cputimer() will set ->running = true again and call
thread_group_cputime(). But since we do not hold tasklist or
siglock, we can race with fork/exit and copy the wrong results
into cputimer->cputime.
It is unneeded because if ->running == true we can just use
the numbers in cputimer->cputime we already have.
Change fastpath_timer_check() to copy cputimer->cputime into
the local variable under cputimer->lock. We do not re-check
->running under cputimer->lock, run_posix_cpu_timers() does
this check later.
Note: we can add more optimizations on top of this change.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100611180446.GA13025@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/posix-cpu-timers.c')
-rw-r--r-- | kernel/posix-cpu-timers.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index d5dbef5e89e6..f66bdd33a6c6 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -1287,7 +1287,10 @@ static inline int fastpath_timer_check(struct task_struct *tsk) if (sig->cputimer.running) { struct task_cputime group_sample; - thread_group_cputimer(tsk, &group_sample); + spin_lock(&sig->cputimer.lock); + group_sample = sig->cputimer.cputime; + spin_unlock(&sig->cputimer.lock); + if (task_cputime_expired(&group_sample, &sig->cputime_expires)) return 1; } |